Adhesives used in the electronic packaging industry typically contain a thermosetting resin combined with a filler and some type of curing initiator. These resins are primarily used in the electronics industry for the preparation of non-hermetic electronic packages. Adhesives useful for electronic packaging applications typically exhibit properties such as good mechanical strength, curing properties that do not affect the function of the component or the carrier, and rheological properties compatible with application to microelectronic and semiconductor components. Examples of such packages are ball grid array (BGA) assemblies, super ball grid arrays, IC memory cards, chip carriers, hybrid circuits, chip-on-board, multi-chip modules, pin grid arrays, and the like.
One area of continuing research in the electronic packaging industry is the development of low stress, high Tg adhesives. It is well known that glass transition (Tg) temperatures can be readily increased through the use of polyfunctional monomers. One, often very undesirable, consequence of the use of such polyfunctional monomers is that both cure stress and modulus are also significantly increased. Thus, the use of high levels of polyfunctional monomers to boost the Tg of thermoset adhesives can often be counter productive in terms of the final cured properties of the adhesive. It would be very useful to have high Tg monofunctional monomers. These compounds could be used to lower crosslink density while preserving or, in many cases, increasing the glass transition temperature of the adhesive formulation. Therefore, it is desirable to have a thermoset with a high Tg and a low crosslink density. A higher Tg will retain the lower coefficient of thermal expansion (CTE) of α1 (i.e. the low CTE that exists prior to the Tg). A thermoset adhesive with a high Tg and a low cross-link density is considered superior because this combination results in lower interfacial stress.